Electronic structure and optical absorbance of doped amorphous silicon slabs

Authors

  • Jessica J. Ramirez,

    1. Department of Chemistry, Quantum Theory Project, University of Florida, Gainesville, FL 32611
    Current affiliation:
    1. Los Alamos National Lab, New Mexico, USA
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  • Dmitri S. Kilin,

    1. Department of Chemistry, University of South Dakota, Vermillion, SD 57069
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  • David A. Micha

    Corresponding author
    1. Department of Chemistry, Quantum Theory Project, University of Florida, Gainesville, FL 32611
    2. Department of Physics, Quantum Theory Project, University of Florida, Gainesville, FL 32611
    • Department of Chemistry, Quantum Theory Project, University of Florida, Gainesville, FL 32611
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Abstract

The absorption of light by doped amorphous silicon (a-Si) slabs, in the far IR to near UV spectral range, has been calculated using molecular dynamics and density functional theory for extended systems. Our systems were modeled by supercells and with periodic boundary conditions. A series of 10-layer, each with 6 × 4 Si atoms, a-Si models were generated via simulated melting and quenching, followed by passivation of the top and bottom surfaces by hydrogen atoms. Our supercells were constructed with substitutional doping of Si lattice atoms, at densities of about 0.5–1.0% dopant atoms per surface unit, converting the a-Si slabs into either p-type (using Group III elements: B, Al, Ga) or n-type (using Group V elements: N, P, As) systems. Results obtained include geometry conformations, density of states, electronic band gaps, and excitation spectra. They have been compared with previously obtained values for crystalline versions (c-Si) of the systems mentioned above. We find that for both the amorphous and crystalline sets, doping reduces the bandgap from the pure silicon value, as acceptor/donor levels are introduced by defects into the Si bandgap region. This also reduces the HOMO-LUMO energy gaps and allows for absorption at new wavelengths. Compared to pure Si, doping appears to significantly increase absorption intensity for lower-energy radiation, as well as induce the wavelength of the absorption maximum to red-shift. Computational investigations of this type provide fundamental insight on properties of materials pertinent to photovoltaic devices. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012

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